ON RADAR:Tamerlan Tsarnaev, who with brother Dzhokhar staged the bombing, was put on the terror watch list but got back into the country.

ON RADAR: Tamerlan Tsarnaev (above), who with brother Dzhokhar staged the bombing, was put on the terror watch list but got back into the country.

ON RADAR: Tamerlan Tsarnaev (left), who with brother Dzhokhar staged the bombing, was put on the terror watch list but got back into the country. (
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The Boston Marathon bombers set off their deadly explosives with a simple device found in a kid’s toy box — a remote control for a play car, it was revealed yesterday.

The remote, which included a transmitter powered by a rechargeable “C” battery, was found among the debris of the pressure-cooker bombs planted by brothers Tamerlan and Dzhokhar Tsarnaev, said Congressman Dutch Ruppersberger.

The Maryland Democrat said the FBI revealed the detonation system during a briefing about the April 15 attack, which killed three and injured more than 200.

“It was a remote control for toy cars,” Ruppersberger said. “Which says to me . . . they got the information on how to build the bomb from Inspire magazine.”

Inspire, an English-language online magazine published by al Qaeda, was cited by Dzhokhar, 19, as a blueprint for the bombs.

It published an article on pressure-cooker bombs in 2010 called “How to Make a Bomb in the Kitchen of Your Mom.”

Also yesterday:

* Before the terror blasts, CIA officials warned the FBI that Tamerlan was meeting with “some seriously dangerous people in Russia and he was ready to become a jihadist,” a law-enforcement source told The Post yesterday.

CIA officials also asked the FBI to place Tamerlan on an international terror watch list, which was done. But, despite the warnings, no red flags were raised when Tamerlan returned from Russia and he was let back into the United States.

* NYPD Commissioner Ray Kelly said that Dzhokhar, from his Boston hospital bed, told authorities that after the bombings he and Tamerlan planned to go to New York City “to party.” Their post-bombing escape plan was thwarted when Tamerlan was killed in a police shootout early Friday, and Dzhokhar was nabbed that night.

* The brothers’ parents — who have claimed their sons could not have committed the attack — said they will travel from the Russian Republic of Dagestan to the United States today. Yesterday, US investigators interviewed the mother, Zubeidat Tsarnaev, in Dagestan. She is wanted for allegedly jumping bail on shoplifting charges.

* The area around the marathon finish line on Boston’s Boylston Street — which had been closed off since the attack — reopened, with fresh concrete poured over the damaged sidewalk.

* It was revealed that Katherine Russell, Tamerlan’s Muslim-convert wife, was arrested in 2007 for swiping goods from a Warwick, RI, Old Navy store. The case was dismissed after she completed community service.

* Neil Diamond will donate proceeds from his song “Sweet Caroline” to victims of the bombing after sales of the Fenway Park anthem soared nearly 600 percent this week.

* Dzhokhar’s classmates at the University of Massachusetts Dartmouth told the Boston Globe that he sold pot, and that his dorm room reeked of marijuana.

* Officials said yesterday that there was no gun recovered from the boat where Dzhokhar was hiding in Watertown, Mass. Authorities had previously said Dzhokhar had exchanged gunfire with them in the dramatic capture.

CIA warnings about Tamerlan prompted inquiries as to whether he should have been under more intense scrutiny.

“We’re going to get to the bottom of it,” vowed House Speaker John Boehner (R-Ohio), saying hearings would be held on how federal agencies handled the warnings.

“I think we want to understand exactly what happened and what didn’t happen and hold those responsible if in fact there were opportunities to stop these people when we didn’t do it.”

In Russia, mom Zubeidat told CNN, “If they are going to kill [Dzhokhar], I don’t care.”

According to Fox News, the FBI claims Tamerlan sent text messages to his mother vowing to die for Islam.

Investigators say Dzhokhar has told them he willingly followed Tamerlan’s lead in planning and executing the bombings. But officials said yesterday those statements were made before the suspect was read his rights.